1. Field of the Invention
The present invention relates to a picture quality improvement device of video signals and a picture quality improvement method of video signals.
2. Description of the Related Art
In an image display device such as a television image receiver or video projector, picture quality is known to deteriorate due to the occurrence of flare. Flare is a phenomenon in which the reflection or scattering of light on the irradiation surface or lens of a picture receiving tube or projector tube causes the intrusion of light of a bright area into the light of a dark area, thereby producing the blurring of edges at which the differences in the luminance of a displayed image are great (for example, at the borders of white regions and black regions).
To correct this type of flare, image processing is carried out to emphasize edges having large differences in luminance in a displayed image. Referring to FIG. 1, a block diagram is shown that shows an example of the configuration of a picture quality improvement device of the prior art for correcting flare by an image process for emphasizing edges (Refer to JP-A-H01-246984 (Patent Document 1) or JP-A-H01-246985 (Patent Document 2)). In FIG. 1, image processing is carried out to emphasize edges for the G signal of RGB (Red, Green, and Blue) signals.
In FIG. 1, G input signal (Gin) is supplied as input to delay compensation circuit 22 and two-dimensional low-pass filter (LPF) circuit 23. Delay compensation circuit 22 is a circuit for delaying the input signal the time required for the processing of two-dimensional LPF circuit 23 (the same being true of delay compensation circuit 21 and delay compensation circuit 27). Two-dimensional LPF circuit 23 is a filter for eliminating from the input signal frequency components (such as edge components) that are higher than a prescribed frequency. Two-dimensional LPF circuit 23 is made up from, for example, a delay circuit, an amplification circuit, and an addition circuit; and eliminates the high-frequency component of the input signal by replacing the data of a particular picture element with, for example, the weighted average of data of a plurality of adjacent picture elements (refer to Patent Document 2).
Due to the elimination of the high-frequency component of the G input signal that is applied as input to two-dimensional LPF circuit 23, a signal in which edges are dulled is supplied as output from two-dimensional LPF circuit 23 (refer to the waveform shown in FIG. 1). The G input signal that has been delayed by delay compensation circuit 22 a time interval that corresponds to the processing time of two-dimensional LPF circuit 23 and a signal in which edges have been dulled that is supplied as output from two-dimensional LPF circuit 23 are applied as input to subtraction circuit 24. Subtraction circuit 24 supplies as output a signal in which the latter signal is subtracted from the former signal. Accordingly, subtraction circuit 24 supplies as output a signal in which the high-frequency component (edge component) that was eliminated by two-dimensional LPF circuit 23 has been extracted. Amplification circuit 25 multiplies the signal in which the high-frequency component has been extracted by a prescribed factor and supplies this signal to addition circuit 26. Addition circuit 26 adds the signal in which the high-frequency component has been extracted, that has been multiplied by a prescribed factor, and that has been supplied as output from amplification circuit 25, to the G input signal that is supplied from delay compensation circuit 22. As a result, the G output signal (Gout) is a signal in which the edge component of the G input signal has been emphasized. The above-described process thus realizes flare correction.
In the foregoing explanation, flare correction is carried out only for the G signal because, of the RGB signals, flare correction in the G signal has the greatest effect on picture quality improvement. Obviously, flare correction may also be carried out not only for the G signal but for the R signal and B signal as well. Flare correction may also be carried out for the Y (luminance) signal and the color difference signal (in which case, flare correction for the Y signal has a greater effect on picture quality improvement).
The foregoing explanation concerned a case in which the input signal was transmitted by a single phase, but when a large amount of information is transmitted in the signal, and particularly for RGB data, the input signal is transmitted in two phases (the signal is not often transmitted in two phases for Y data or for color difference data). In the following explanation, a signal that is transmitted in two phases is referred to as a “two-phase signal.”
Referring to FIG. 2, a schematic diagram is shown for explaining a two-phase signal. In a two-phase signal, a first-phase data string s1, s2, s3, . . . and a second-phase data string t1, t2, t3, . . . are transmitted at the same clock, as shown in FIG. 2 (showing the case for a one-dimensional video signal). Data sn is the data of the picture element that is interposed between the picture element of data tn−1 and the picture element of data tn. In other words, the data of adjacent picture elements are distributed in order to different phases.
When the input signal is a two-phase signal, flare correction cannot be carried out for each phase independently due to the extremely low accuracy of the extraction of high-frequency components by means of the two-dimensional LPF circuits and subtraction circuits, even when flare correction is carried out for each phase independently.
Thus, in order to carry out flare correction when the input signal is a two-phase signal, the most straightforward approach is to adopt a configuration in which the two-phase signal is multiplexed as a one-phase signal (data of the second phase are inserted into data of the first phase. In the example of FIG. 2, this insertion would yield the data string: s1, t1, s2, t2, s3, t3, . . . ), flare correction carried out by means of a picture quality improvement device of the prior art, and the output signal then resolved to a two-phase signal (the data of adjacent picture elements are distributed in order to different phases). FIG. 3 is a block diagram showing the configuration of a picture quality improvement device for a case in which the input signal is a two-phase signal. The input two-phase signals for R, G, and B are applied as input to multiplexers MUX31, MUX32, and MUX33, respectively, and multiplexed. Flare correction is then carried out for the multiplexed single-phase signals (flare correction is performed for only the G signal in FIG. 4), following which the single-phase signals are each resolved to two-phase signals in demultiplexers DEMUX 34, DEMUX 35, and DEMUX 36 and then supplied as output.
In the picture quality improvement device of FIG. 3, flare correction is carried out for a single-phase signal that has been multiplexed, and the elements from MUX to DEMUX must therefore be operated at a clock frequency that is twice the clock frequency of the two-phase signal. However, the original reason for transmitting by a two-phase signal was the excessive clock frequency required for transmission by a single-phase signal. Carrying out flare correction for the multiplexed single-phase signal therefore demands high-speed operation in the elements between the MUX and the DEMUX, and in particular, the two-dimensional LPF circuits, and consequently imposes a great load upon these elements.